Treatment of aromatic and unsaturated distillates



Jap. 22, 1957 D. s. MAlsl-:L ET AL 2,778,863

TREATMENT OF AROMATIC AND UNSATURATED DISTILLATES Filed March 19. 1952 United States Patent O TREATNIENT OF AROMATIC AND UNSATURATED DISTELATES Daniel S. Maisel, Union, and Brook I. Smith and Harold W. Scheeline, Elizabeth, N. J., assignors to Esso Research and Engineering Company, a corporation of Delaware Application March 19, 1952, Serial No. 277,486

4 Claims. (Cl. 260-674) The present invention relates to improvements in successive clay treating and fractionation operations imposed on aromatic and highly unsaturated naphtha distillates for the production of valuable polymers from unsaturated components while recovering separate benzene and toluene concentrates suitable for extractive distillation.

Substantial revisions, made in accordance with the present invention, have been successful in greatly reducing the fouling of thev clay, improving the quality and recovery of polymerl and for obtaining appropriate aromatic concentrates suitable for extractive distillation with the various solvents such as phenolic solvents, furfural, triethylene glycol, etc. j

The main improvement features of the present invention are as follows: v p

(a) Operation of an initial mild clay treatment to which the naphtha distillate is subjected substantially in the liquid phase so that only a portion of the diolefnic components that are'lmost reactive form polymers and the polymers as they are formed are removed fromv the clay continuously by the remaining unpolymen'zed liquid components of the distillate. By this improved operation the clay bed run lengths are extended from an earlier life` period of 8-15 days to life periods of 40-60 days and the yield of high quality polymer is enhanced.

(b) The` clay treated aromatic distillate carrying along the polymer washed from the clay is subjected to a steam distillation for separating the polymer as a bottoms product, and fractionation for removal of a heavy naphtha fraction as a` side stream product during recovery of light naphtha overhead distillate containing substantially all of the benzene and toluene. l (c) The 'light aromatic distillate separated from water is subjected to a second fractionation to obtain a suitable benzene concentrate that needs no further treatment prior to extractive distillation and into a toluene fraction. The toluene fraction, however, is subjected to a second clay treatment under mild conditions similar to the initial clay treatment to form additional polymer which is separated by further fractionation in the absence of water vapor. This fractionation to recover additional polymer from the lsecond clay treatment gives the toluene distillate a more nely adjusted end point.

The features` .of this invention will be describedl in f greater detail'with reference to the accompanying drawing, which shows schematically the ow plan for a preferred arrangement of process means.

, In the drawing, the naphtha feed lcontaining largely unsaturated hydrocarbons with 20 vto 30 volume percent of aromatics is passed from line 1 through preheating means 2 into the clay treating drum 3.

but alternatively the liquid naphtha may be passed downwardly through the clay. The eluent treated naphthav hydrocarbons carrying in solution the polymers formed from the reactive diolelins is passed from the clay treating drum 3 through line 4 into kan intermediate part of the fractionating column 5. About tive plates above the feed inlet point, a side stream of heavy naphtha is withdrawn by line 6 to a stripper 7, at the bottom of which is introduced steam from line 8 for stripping light naphtha components. The light naphtha components vaporized at about 290-320 P. in the stripper 7 are returned a few `plates above the point at which the side stream l is removed by line 9. Stripped heavy naphtha at 260-420 F. boiling range is withdrawn by line 10. The light naphtha vapors including substantially all of the benzene and toluene, are taken overhead by line 11 to a cooling condenser 12.

The aqueous overhead distillate isrun from condenser 12 into a receiver 13, where a bottom water phase is separated to be removed by line 14. Some of the upper hydrocarbon phase distillate is returned as reflux through line 15 at about the 16th plate above the feed inlet. The remaining light naphtha overhead distillate separated from water in receiver 13 is passed by line 16 to the next fractionating column 17.

For satisfactory distillation in column 5, i. e., for collecting the polymers as a finished bottoms product and taking overhead substantially all benzene and toluene, it`

is important to supply large amounts of steam as a stripping agent, e. g.V by line 18 as well as by line 8. The total steam supplied to column 5 amounts to about'S to 20 wt. percent of the hydrocarbon feed, including steam used in the side stream stripper 7, the latter being at least about 1/3 to 1/2 of the total used. With these amounts of steam in `column 5, the bottoms polymer product is prevented from being decomposed by overheating while it is stripped freek of original naphtha components. Some of the polymer bottoms is withdrawn by line 19 through the reboiler 20 to supply additional heat for the distillation at temperatures of 380-420 F. The nal bottoms polymer is withdrawn by line 21. In the second fractionating column 17, the feed inlet plate is about l5 plates above the bottom to provide a stripping action in which the toluene cut is substantially freed of benzene and any dissolved water.

A benzene cut free of toluene is Withdrawn'at about 20 plates above the feed inlet plate through line 22. The benzene cut withdrawn will contain no more than a trace of water'and may be sent directly to storage tank 23 prior to a subsequent extractive distillation for puriication. This benzene cut needs no further treatment prior to extractive distillation.

The overhead vapors from column 17 contain hydrocarbons boiling up to F. with a slight amount of water vapor and are passed by line 24 through a cooling condenser 25 to supply reflux condensate which is returned from receiver 26 to column 17 by line 27 at about 25 or 30 plates above the feed inlet plate. The overhead distillate boiling below 165 F. will contain less than 3% benzene with certain diolens preferred to be removed from the system by line 28. The second fractionator serves to dry thearomatic Vj concentrates while making the precise cuts desired. The

`Patented Jan. 22, 1957i i It is advanl tageous to pass the liquid naphtha upwardly through the clay bed for more effective liquid-with-clayvcontacting,

line: 29. A portion offthe'- bottoms may be recycled through a1 heat exchange reboiler 30 and linel 31 -to supply heat needed iu columnl17.

The toluene-rich bottoms from column 17 is passed by line131 into-vabottomapart off'tlie secondic-lay-treatin'g` 5 drum 33, wherein tlietoluenefactionisitreatedunder conditionsfsirnilarfto =those'used"in the first treating'- drum 3: Hereagain, theclay treateditolueneLriehvhydroeare bonsA wash awa-y polymers formed'v during the'A secondclay treatment; and the -eilluent 'liquidf hydrocarbons'I containingy the-polymersfarelpassed byline 34T into the third fractienator or rerun column 357 aboutifour platesabove theb'ottorn; The toluene concentratedistillate'is-drawn overhead-distillate'is returned bylinef'3'95as re'ux to ay top plaite-whieh=is=about the lth-l4thplate above/theV feed inlet; The 1 remaining portionof `the Aoverhead dis-- tillate isL sent by I`line 4407A to storage tank` 41u for Ysubsequent purification operations. The `polymers derived from` the second clay' treatment are withdrawn asy a-k bottomsproduct from column 29 through line-42.

The-initial feedstock suitable for the treatment-is a debutaniiedcraeked naphtha boiling V-in the yrange 'of from about' 120; F. to' 420 F. with the following kind; of composition:

Components: Volume .percentvv Parains 2'- 5 Ol'ens- 45;-70 Benzene lOl-1'5" Toluene -15'y Dioleiins 10-20 Temperature, 250 F.-3'50 F;

Feed Rate, 0.2540- v../v:/hr. (vol. ofi" liquid/vol. of

clay/hn).

Pressures, 70-200 poundsV per square inch gauge.

The mainrequirements in .treating .suchr a wideboli'ng. naphtha ,fraction withfclay so that the polymerstormed are extracted and .washed .awayf-rom .the clay, are;

(l) The hydrocanbonscontactedwith the. clay, under. the conditions of contact, must remainsubstantiallyin the. liquid phase,y preferably with. amaximum vtemperaturc of'350 Under .these'conditions..approximatelyI` only about half the diolens becomepolymerized,` but the unreacted veompouentsof Ythefeed..stoekare then in suiiicientquantity t-o extract. and carryaway thelpolymers as. they areformed Thisinital claygtreatment is carried out primarily to form polymerslthatsuitablytmeet:specification requirements. More intense polymerization-"x of the diolens at this/stage:is-adverseto they tpla-lityv of the polymenand. causes-fouling: of. the clay.

The eluentliquidwithdrawnfrom the clay/treating drum .3 by line; 4, should 4have a-lcomposition exemplied as follows:

Table II.-Im'tial clayjtreat effizient products TOTAL EFFLUBNT' Components Vlumefpercent' Polymer SL10 Paraflns` 2- 5" 4 Benzene 10`-'20 Toluene t 11)-20 Olens 45-70 Diolens 5-10 The eiluent from the=initial clay treating unit can be made to ow directly into a rst fractionating column, column" 5,- to Lb'efractionated in' suchla-manner that'the polymers are recovered' as a bottoms product, while the benzene fand toluene are taken overhead. as a distillate with stripping steam. In this operation of segregating the polymerprodnct, .an intermediate fraction boilingfin the range of 260-420 F., and termed a heavy naphtha fraction, is withdrawn. as. a side. stream. To avoid any loss of'toluene in the heavy naphtha side stream, this heavy naphtha isstripped With av controlled amount of steam in order to return toluene back to the fractionating column, thus giving the heavy naphtha an initial boiling point of 'about 260 F; and makingthe lossI 'of'toluene less than.5%.

The polymer bottoms which canbe withdrawn' from the fractionatingV column 3 are suitable directlyfor many uses. For Vexample, these .polymers meetspeciiiere'quire-` ments for use as a rubber extender' or'as a core.oil. They have suitable viscosity and light color.

Satisfactoryoperating conditions for column 5 in which polymer is segregated from an intermediate heavy uaphtha fractionand the light naphtha distillate are as follows:

Top or'overhead vapor: temperature, 2'60'290 F." Pressure, 40-80'p'ounds `p'ersq. inch` absolute. Bottoms temperature, 380 F.460 F.'

The'light naphtha distillate taken overheadfromfcolumn 5; should have a'na'l'end point inthe-range of 240 F.I and 290 F. and have a composition which comes within" the 'following .ranges-z Table JIL-Composition. of lghtlnaphtha distillate" (dry)` for splitting into Abenzenev and 'toluene cuts Components: Volume vpercent Paraflins l.`-5 Olens 40`-60 Benzene l`S-2`5" Toluene 15-25 Diolen's 4"-8 The lightI naphtha with a'V composition above-described after'rem'oval of as much water as practical by vphase separati'on; .can -be eiiciently-'split intoY a benzeneconcentrate intermediate-fraction which is quitesuitablerfor extractive distillation anda toluene bottoms fraction having agproperly adjusted endpoint for further treatment.' The split# ting between the benzene and tolueneJfi-actionsA is carried out'in a 'secondfractionatingv columnl17rv which hasbeen termedilaf splitten This@ columnisefficiently operated under a pressure ofy about '.1001p. s. i. g."- witli'fa'bottom temperatureof 380 F.v and'a top oroverheadftemperm turesof about' 165 F. With thiswoperationtheoverhead componentsA will=inc1ude a' `srnall amount-of'water, less than about 3% benzene, and some dioleiirs'.l hydrocarbon. composition'- of* theoverhead'fis typified` by v4the following.

Table. I V.-Sp'li tter overhead:

trace of water will have the following type of composition:

Table V.Benzene concentrate Components: Volume percent Parafns 1-5 Benzene 30-50 Dioletins 2-8 Olelins 40-65 Toluene The desired water-free toluene bottoms fraction from the splitter will have a composition as follows:

Table VI.-Splz'tter bottoms-toluene fraction [Boiling range 185-260 F.]

Components: Volume percent Paraflins 1-5 Toluene 25-45 Benzene 1-3 Olefns 45-70 `Diolet`ms 4-10 under 70-200 pounds per square inch gauge and atl 250-350 F., and aliquid ow rate of 0.25 to 10 vols/vol. of clay/hr. With this clay treatment, the effluent from the treated toluene fraction will have the following composition:

y Table VIL- Clay treated toluene fraction ejluent Components: Volume percent Polymer 2-8 Parains 1-5 Olens 40-65 Diolens 1-3 Benzene 1-3 Toluene 30-50 As in the initial clay treatment, again it becomes necessary to separate the toluene from the polymer that4 is washed away from the clay and this function is served by the toluene concentrating column 35 operated with a top temperature of about 240-300 F., under a pressure of 40 p. s. i. g. and with a bottom temperature of about 380 F.' The iinal toluene concentrate is now fully preconditioned for extractive distillation and will have a composition of the following type:

Table VEL-Final toluene concentrate [Boiling range 185-240 F.]

Components: V'olume percent Parains 1-5 Toluene 30-50 Benzene 1-3 Olens 40-65 Diolens 1-3 The details of vapor-liquid extractions or extractiva distillations are well-known and need not be discussed at length here.

It is to be noted that the present invention is concerned with the steps to be taken in segregating three main products from a highly cracked naphtha, namely, high quality polymer derivatives of diolens present in the naphtha, a benzene concentrate suitable for extractive distillation, and a toluene concentrate suitable for extractive distillation. In this process, certain advantages are gained 6 1 in preconditioning the benzene concentrate while the toluene is also undergoing a partial preconditioning, such as occurs in the initial clay treatment followed by successive fractionation in two columns, the rst column being used to segregate a high premium polymer productand intermediate heavy naphtha fraction with the aid of steam, the second column making a split between the desired benzene concentrate and bottoms toluene fraction substantially free of water. With the described treatment, a premium quality polymer is obtained from the more highly reactive diolefins under conditions for length ening the clay life, using any of the well known polymerizing clays, e. g. activated bentonite, Attapulgus clay, fullers earth, Supertltrol, Floridin, etc.

Although the second clay treatment 'imposed on the liquid toluene cut does not form polymer product of as high quality as the first clay treatment, it has to be controlled for long clay life. The factors contributing to long life of the clay in this second treatment are the narrow boiling range of the toluene fraction treated, the mildness of conditions in the treatment, and quick removal of polymers formed with the liquid hydrocarbons treated. 'I'he polymer product separated from the second clay treatment efuent'is `diluted and fluxed by hydrocarbons boiling above 240 F. to reduce its viscosity.

It is to be understood that modications may be made without departing from the spirit and scope of the invention. Although the hydrocarbon fractions are preferably maintained in the liquid phase in the clay treatments to obtain extended life of the clay, the hydrocarbon fractions may be in a mixed-vapor phase or in vapor phase in each of the clay treatments while making use of the first fractionator land second fractionator as described.

When subjecting the hydrocarbon fractions in a mixed phase or vapor phase to the clay treatments, the ternperature of the clay may be in the range of 250 F. to about 500 F. and the hydrocarbons may be passed more rapidly through the clay treating zone as the temperature is raised.

In any event, the clay treated hydrocarbons have to be separated from the resulting polymers formed in the first clay treating zone by using steam in the first fractionating zone where the polymers are removed a's a bottoms product. It thus becomes important to eliminate Water condensed from the steam so that in the subsequent fractionation for segregating the aromatic concentrate fractions, either the Cs aromatic or C7 aromatic concentrate, these fractions are kept substantially free of water.

What is claimed is:

1. In a process for segregating Cs an-d C7 aromatic hydrocarbon concentrates suitably freed of reactive diolens for extractive distillation from a naphtha containing mainly olenic and aromatic hydrocarbons, the steps which comprise contacting said naphtha in liquid phase with clay at 250 F. to about 500 F.; passing the claytreated naptha and resulting polymers of reactive diolens from the clay into a rst fractional distillation zone; distilling a light distillate portion of the clay-treated naphtha hydrocarbons containing the aromatic hydrocarbons to be segregated from said polymers with added steam in said first distillation zone; substantially freeing the light distillate of water; passing the said light hydrocarbon distillate substantially free of water into a second fractional distillation zone; separating in said second fractional distillation zone concentrates of C6 and C'z aromatic hydrocarbons, the Ca aromatic concentrate beinga water-free distillate boiling in the range of to F.; then subjecting said Cs aromatic concentrate to an extractive distillation to recover purified benzene.

2. In a process for segregating a benzene concentrate suitably freed of reactive diolefins for extractive distillation from a cracked naphtha containing mainly olenic and aromatic hydrocarbons, the steps which comprise contacting a fraction of the naphtha boiling in the range of about 120 F. to 420 F. with clay at 250 F. to 350 a secondfractional.distillation. zone to removev overhead dissolvewaterwith. hydrocarbonstliat boil up to 165 F.;.withdrawing .as an intermediate, cut from said second fractional distillation zone a Waterffree benzene concentrate, fraction that boilsinthe. range. of 165 F. to. 185

F., and a bottomsicut. containing.. hydrocarbonsboiling above. 185 f F.; then subjecting s said. benzene. concentrate tof-a'-subsequent.,extractive. distillation to obtain purified benzene.` 1

3. In a process.v for segregating. benzene and. toluene concentrates..freed. of reactive. diolens and. recovering polymers derived froms-aidreactive dioleiins inacracked naphtha fractionI containing. mainly unsaturated hydro carbons with aromatic hydrocarbons, the steps which.

comprise contacting. the naphthafraction.boiling inthe rangeofapproximately 120 E to 420' F. andessentially including thebenzene and toluene inliquid-phase. withY clay attemperatures of 250 to 350 F.; owing theliquid phase naphtha hydrocarbons through the clay, to carry therefrom polymers derived from the reactive di* olefin componentsfin said naphtha; passing the. resulting liquid mixture of the clay-treated naphtha and polymers into avrst fractional ydistillation zone.; introducing. steam at a bottom part of.saiddistillationzone;.separatingoverf head.. from the first fractional distillation zone a light naphtha distillate fraction. containing the. benzene and toluene; withdrawing a heavy naphtha fraction. boiling.

above 2609 F. from an intermediatey part. of said.. zone;

withdrawing saidl'polymers as bottomsproduct; seltxarating. water from the light naphtha distillate fraction; passing. said light naphtha distillate from said lrst fractionation zone into a second fractionation. zone; operating said secondffractionation Yzone to. distill.` overhead aV light frac.- tiony containinghydrocarbons.. that,.boil below-165 F.; recovering from `said second.fractionatiomzone a benzene concentrate boiling intherange from 165 F. to 185 F. asan'intermediate distillate fraction; and recoveringl a" bottoms toluene fraction boiling in the range of 185 F. to 260 F. from said second fractionation zone; and subjectingaid. benzene concentrate to an extractive'distillation to. obtainpnritied. benzene.

4.- In a. process for. segregating.. benzene and toluene concentrates. suitably freedv of. reactive dioleiins .for eX- trac-tive distillation of said concentrates and for recovering polymersv from said reactive diolelins in a cracked naphtha, which. comprisw contacting a fraction of the cracked naphthaboiling in the range of about F. to 420 F. in liquid phase with clay at temperatures of 250 Fi to350? F; and'contact time controlled to form polymers from about.'half:the diolenfcornponents of the naphtha fraction; passing the clay-treated naphtha hydrocarbons and the polymers into a rst fractional distillation zone; distilling a light fraction having a nal boiling point ofab'out' 260 F.` containing benzene and toluene with stearnfrom said'distillation zone; separating the distilled hydrocarbons from water in the distillate ofsaid-.distillation zone; passing the separated hydrocarbon distillate into a second.` fractional distillation zone; withdrawing from` said second distillation zone van overhead' boiling below o F., anintermediate cut containing benzene boi-ling' between 165? F.-185"-'F. and a bottoms residue boiling/from about F. to aboutA 260 F. containing the' toluene substantially freey of benzene and free of water;v passing said Vbottomsl residuel in liquid phase througha secondbedfofclay'at 250' F. to 350 FQ; and* distil'ling a toluene concentratev boiling in the range ofV 185 FJ' toy 2`40`` F. from efiiuent liquid containing' polymers removedfrom the second vclay A bed.

Refrencesi-Cited-in thele of this patent UNITED'STATES PATENTS 

1. IN A PROCESS FOR SEGREGATING C6 AND C7 AROMATIC HYDROCARBON CONCENTRATES SUITABLY FREED OF REACTIVE DIOLEFINS FOR EXTRACTIVE DISTILLATION FROM A NAPHTHA CONTAINING MAINLY OLEFINIC AND AROMATIC HYDROCARBONS, TH STEPS WHICH COMPRISE CONTACTING SAID NAPTHA IN LIQUID PHASE WITH CLAY AT 250*F. TO ABOUT 500*F.; PASSING THE CLAYTREATED NAPHA AND RESULTING POLYMERS OF RACTIVE DIOLEFINS FROM THE CLAY INTO A FIRST FRACTIONAL DISTILLATION NAPHTHA HYDROCARBONS CONTAINING THE AROMATIC HYDROCARBONS TO BE SEGREGATED FROM SAID POLYMERS WITH ADDED STREAM IN SAID FIRST DISTILLATION ZONE; SUBSTANTIALLY FREEING THE LIGHT DISTILLATE OF WATER; PASSING THE SAID LIGHT HYDROCARBON DISTILLATED SUBSTANTIALLY FREE OF WATER INTO A SECOND FRACTIONAL DISTILLATION ZONE; SEPARATING IN SAID SECOND FRACTIONAL DISTILLATION ZONE CONCENTRATES OF C6 AND C7 AROMATIC HYDROCARBONS, THE C5 AROMATIC CONCENTRATES BEING A WATER-FREE DISTILLATE BOILING IN THE RANGE OF 165* TO 185* F.; THEN SUBJECTING SAID C3 AROMATIC CONCENTRATE TO AN EXTRACTIVE DISTILLATION TO RECOVER PURIFIED BENZENE. 